There are known porous monoliths having pores and composed of an inorganic material such as silica. Such monoliths are widely used in chromatography separation columns, enzyme carriers, catalyst carriers, etc. For production of such porous monoliths, a sol-gel method, which is a liquid-phase reaction method, is generally used. The sol-gel method refers to a method in which: an inorganic low-molecular compound having a hydrolyzable functional group and dispersed in a dispersion medium is used as a starting material; and an aggregate or a polymer of an oxide is obtained by a sol-gel reaction, that is, by hydrolysis of the compound followed by polycondensation. The inorganic low-molecular compound as the starting material is, for example, a metal alkoxide, a metal chloride, or a metal salt having a hydrolyzable functional group.
Conventional common porous monoliths usually have only mesopores (pores having a diameter of 2 nm or more and less than 50 nm). Such porous monoliths do not necessarily posses characteristics required for various applications. Patent Literature 1 (WO 03/002458 A1) discloses a method of producing a porous monolith having mesopores with a narrow pore size distribution and further having controlled macropores (pores having a diameter of 50 nm or more) by adjusting the conditions of a sol-gel reaction so that the sol-gel transition and the phase separation simultaneously take place.
Patent Literature 2 (WO 2007/021037 A1) discloses a method for producing a porous monolith that has a framework composed of titanium dioxide (TiO2) and has controlled mesopores and macropores. The method disclosed in Patent Literature 2 can yield, based on the method disclosed in Patent Literature 1, a porous monolith of titanium dioxide which is a titanium compound in the case of which the pores are difficult to control by conventional sol-gel methods due to very high hydrolyzability of the inorganic low-molecular compound used (e.g., an alkoxide).
However, there are very few disclosures relating to a method for producing a porous monolith composed of a titanium compound other than titanium dioxide. Non Patent Literature 1 disclosing such a method specifically discloses a method including: mixing a titanium dioxide powder and an organic solvent containing a polymer material acting as a template for macropores; molding and sintering the resulting mixture; and subjecting the resulting porous monolith to a reducing treatment using hydrogen to introduce oxygen deficiency in the monolith. This porous monolith has electron conductivity derived from the oxygen-deficient titanium oxide. Judging from the production method, however, it is considered that the porous monolith produced by this method is basically a powder aggregate, has only macropores formed by burning off of the polymer material dispersed in the mixture, and does not have controlled macropores. Furthermore, although in this porous monolith the particles of the oxygen-deficient titanium oxide powder are bound together, a single crystalline phase of the oxygen-deficient titanium oxide is not thought to be achieved.